The present invention relates to extrusion methods, in particular for shaping polymer solutions or polymer fluids.
Cellulose and other polymers can be dissolved in suitable solvents and transferred by controlled solidification into a desired shaped article. If this shaped article is constituted by fibres, fibrils and the like, reference is also made to a spinning process. Cellulose is dissolved for example in aqueous solutions of amine oxides, in particular solutions of N-methylmorpholine N-oxide (NMMO), in order to produce spinning products, such as filaments, staple fibres, films, etc., from the obtained spinning solution. This occurs by precipitation of the extrudates in the water or diluted amine oxide solutions once the extrudates of the extrusion die are guided via an air gap into the precipitation bath.
U.S. Pat. No. 4,416,698 relates to an extrusion or spinning method for cellulose solutions in order to shape cellulose into fibres. In this case, a fluid spinning material—a solution of cellulose and NMMO (N-methylmorpholine N-oxide) or other tertiary amines—is shaped by extrusion and brought into a precipitation bath for solidification and expansion. This method is also known as the “lyocell” method.
U.S. Pat. No. 4,246,221 and DE 2913589 describe methods for producing cellulose filaments or films, wherein the cellulose is drawn in fluid form. These documents describe a spinning process in which cellulose is dissolved in tertiary amine oxide, wherein the obtained cellulose solution is pressed via a die, is extruded via an air gap into a spinning funnel, and is discharged at the end of the spinning funnel in the form of continuous fibre. The spinning funnel used is equipped with a feed means and a discharge means for the spinning bath.
A further method is described in U.S. Pat. No. 5,252,284, in which elongate shaping capillaries are used to shape a cellulose material.
WO 93/19230 A1 describes a further development of the lyocell method, in which the cellulose-containing spinning material is cooled immediately after the shaping process before introduction into the precipitation bath.
WO 94/28218 A1 describes a method for producing cellulose filaments, in which a cellulose solution is shaped into a number of strands via a die. These strands are introduced into a precipitation bath (“spinning bath”) through a gap around which gas flows and are discharged continuously.
A shaping device and a further variant of the lyocell method are described in WO 03/057951, wherein the cellulose-containing spinning material, after shaping, is conveyed via a shielding region and then via a cooling region.
In EP 0 430 926 B1, a spinneret with a spinneret head and a spinning plate is presented, wherein the spinning plate consists of a stable carrier plate provided with bores. Spinneret plates, in which spinning capillaries are formed, are inserted into the aforementioned bores.
U.S. Pat. No. 5,171,504 A describes a spinning device for a thermoplastic polymer, wherein the molten polymer, after extrusion, is cooled in an air gap before it passes into a spinning bath. Immediately after extrusion, there is a “thermal conditioning zone” in the air gap, wherein the fibres are held at higher temperatures.
WO 97/38153 A1 relates to a lyocell method, in which two different air fans are used in the air gap and can be operated at the same or different temperature. This air fan is used to produce different levels of moisture in the two gas flows. A hot partial flow and a cold partial flow are not described in this document.
GB 900 099 A describes the spinning of polypropylene fibres by extrusion. This document discloses examples of alternative treatment experiments, in each of which a different temperature was used in the air gap. The simultaneous use of gas flows of different temperature is not described.
The publication “The Temperature of Fibres during Air-Gap Wet Spinning: Cooling by Convection and Evaporation”—Volker Simon (Int. J. Heat Mass Transfer. Vol. 37, No. 7, pp. 1133-1142, 1994) presents courses of events in the spinning process. It is stated that the polymer fed into the air gap contains water and that the water evaporates at the surface of the spinning fibre during the spinning process and this water evaporation has a cooling effect on the spinning fibre. It is concluded that the fibre temperature during extrusion is relatively high and the water concentration in the spinning environment is increased by the evaporation of the water from the fibre.
It is specified that the result is that the water vapour gradient causes the water vapour mass flow to be guided from the fibre in the direction of the surrounding environment. The water evaporation taking place in the filament is enabled by the quantity of water located in the filament, whereby a strong cooling effect, greater than with melt spinning, is produced. In a further statement, it is mentioned that the spinning material used in the NMMO method consists of a non-solvent (water), a solvent (amine oxide=NMMO) and cellulose. The author ultimately comes to the conclusion that the solvent does not evaporate during the shaping process.